Electronic musical instrument simulating a stringed musical instrument

ABSTRACT

An electronic instrument for simulating the sound of a plucked string bass or other stringed instrument is described. The instrument incorporates a circuit in which the shunt resistance of a resistive capacitive phase shift oscillator is varied selectively in order to more closely simulate the sound generated by a stringed instrument, where the string is more taut when first plucked and consequently at a higher pitch than after its vibration has damped. The circuit also incorporates a switching arrangement whereby a note can be played either with a gradual decay following release of the key or with a decay while the key is depressed and a rapid cutoff when the key is released in order to permit the person utilizing the instrument to have effective control over the staccato effect.

United States Patent [19] Kitchen [451 Aug. 20,-1974 [76] lnventor: Harry E. Kitchen, 7910 Woodmont Ave., Bethesda, Md. 20014 22 Filed: Sept. 27, 1972 21 Appl. No.: 292,809

[56] References Cited UNITED STATES PATENTS 3,493,668 Bunger 3,538,804 11/1970 George et al 84/1.01

3,609,203 9/1971 Adachi 84/1.0l

3,697,662 10/1972 Adachi 84/1 .13 3,701,040 10/1972 Borrekik et al 84/125 X T! PK/MARY Primary Examiner-Richard B. Wilkinson Assistant ExaminerStanley J. Witkowski Attorney, Agent, or Firm-Berman, Bishoff & Platt [5 7] ABSTRACT An electronic instrument for simulating the sound of a plucked string bass or other stringed instrument is described. The instrument incorporates a circuit in which the shunt resistance of a resistive capacitive phase shift oscillator is varied selectively in order to more closely simulate the sound generated by a stringed instrument, where the string is more taut when first plucked and consequently at a higher pitch than after its vibration has damped. The circuit also incorporates a switching arrangement whereby a note can be played either with a gradual decay following release of the key or with a decay while the key is depressed and a rapid cutoff when the key is released in order to permit the person utilizing the instrument to have effective control over the staccato effect.

12 Claims, 2 Drawing Figures PATENIEDMZOIBH I 3330.952

FIG- 1.

I n I Prmss I Pnnss I I SHIFT SHIFT I l l OUTPUT (ALSO CONNECTED 70' OTHER oscvuparoes) T1 3 pK/MARY f ELECTRONIC MUSICAL INSTRUMENT SIMULATING A STRINGED MUSICAL INSTRUMENT BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic musical instrument and more particularly relates to a circuit for more closely simulating the sound of a plucked string bass or other stringed instrument.

2. Description of the Prior Art The electronic musical instrument art, as it has developed over the years, and as such instruments have become more popular, has been increasingly more concerned with the closer simulation of the sound created by the true musical instrument and in some cases actually improving upon such sounds. At the same time, there has been concern with providing the user of the electronic instrument with the means for creating the various effects, such as staccato, legato and the like, normally obtainable with the true musical instrument.

For example, in U.S. Pat. No. 3,617,601 to Krueger, a frequency shift is used to compensate for the change in subjective pitch that results when the initial part of a note is perceived loudly by the listener. Thus, Krueger is attempting to improve on the sound of a bass viol, rather than trying to duplicate it.

Another problem which has been faced in the prior art is the large number of circuits which are required to produce the required number of notes and the desired effects. While this problem has been approached in the past, as for example in U.S. Pat. No. 3,048,792 to Krauss, no truly satisfactory solution has yet been found.

Accordingly, it is an object of the present invention to provide an electronic musical instrument which more closely simulates the sound of a plucked string bass or other stringed instrument, while utilizing a relatively small number of parts to produce the required number of notes and desired effects.

A further object of the present invention is to more closely simulate the effect that occurs in a stringed instrument where the string is more taut when first plucked than after its vibration has damped somewhat and consequently the tone is slightly higher in pitch initially than after damping has occurred.

Still a further object of the present invention is to provide an electronic instrument for simulating the sound of a plucked string bass or other stringed instrument wherein the instrument may be played either with a sustain following release of a key to produce a legato effect or with a rapid cutoff when the key is released for creating a true staccato effect.

SUMMARY OF THE INVENTION The present invention is applied to an electronic instrument in which the tones are generated by a resistive-capacitive phase shift oscillator with the resistors in shunt branches, although the invention could be applied to any oscillator in which a resistance is one of the frequency determinimg elements. In order to simulate the higher pitch at the inception of a note when the string is tauter than after its vibration has damped, the resistive element in the oscillator is selectively varied in order to initially provide a higher tone and gradually decrease the pitch of the tone after the key has been released. This is accomplished by utilizing a diode as one of the resistive elements and a charging capacitor which discharges through the diode at a selected rate, thus gradually increasing the resistance of the diode as the capacitor discharges and the current through the diode decreases. A further charging capacitor is provided in the output circuit in order to give a sustain for the note played when it is desired to create a legato effect. A pedal-cancel feature is included by means of a switching transistor which'discharges any capacitors which may have remained charged from a previously played note, when the next note is played. A differentiator may be selectively switched into the output circuit and the switching transistor selectively switched into a different circuit arrangement with the secondary of a transformer in order to provide a sharp cutoff in the output circuit and rapidly terminate a note as desired. This will produce a true staccato effect which the player of the instrument may easily control.

Other features, objects and advantages of the present invention will become apparent to those skilled in the art from a consideration of the following detailed description of a preferred embodiment of the invention, taken in conjunction with the appended drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partly block and partly schematic diagram of the conventional oscillator circuit to which the present invention is applied; and

FIG. 2 is a schematic circuit diagram showing the frequency determining and switching circuits of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. 1, there is shown a conventional resistive capacitive phase shift oscillator 10 comprising shunt resistor 20 connected between points A and B, as one of the frequency determining elements of the oscillator. The output of oscillator 10 is applied to the output terminal through a gate consisting of back to back diodes 11 and 12. The gating signal is applied at point X, between series resistors 16 and 17 to capacitor C connected in parallel with resistor 17. As long as capacitor C is charged up with a positive voltage sufficient to make diodes 11 and 12 conductive, the tone signal generated by oscillator 10 will be applied to the output. However, when capacitor C, is sufficiently discharged, or completely discharged, diodes 11 and 12 will be non-conductive and no signal will appear at the output. As will appear more fully below in the discussion of FIG. 2, resistance 20 is varied according to the present invention in order to provide the effect of a higher pitch at the inception of a note, simulating the true sound of a stringed instrument, while the charging and discharging of capacitor C a is utilized to provide either the legato or staccato effect, as described above. It will be understood that the output terminal shown in FIG. 1 may be connected to additional oscillators in order to provide additional tone signals as desired.

Referring now to FIG. 2, there is shown the preferred embodiment of the present invention, comprising a circuit for generating two tones utilizing the single oscillator shown in FIG. 1. However, it will be understood erated with a single oscillator within the teachings of 3 the present invention, simply by following the principles explained below with respect to FIG. 2. As shown in FIG. 2, the resistive frequency determining portion of oscillator corresponding to resistor 20, connected between points A and B, comprises the series combination of impedance Z variable resistor R diode D and diode D or the series combination of impedance Z,, resistor R and diode D depending upon which of the two notes is selected, as will appear more fully below.

Switches 8, and S are keyboard switches which correspond to a particular note to be played. When either of these switches is depressed, B plus voltage source 40 will be connected in series with resistor R and the primary of transformer T causing current to flow. The secondary of transformer T, may be selectively connected to the base of transistor Q between terminal F or G by switch 15, for a purpose which appears more fully below. Similarly, differentiator 13 may be connected or disconnected from point X by switch 14. Diodes D,, D D D D and D as well as diode D, at times, are isolating diodes which cause the current flow to take only a prescribed path, when either switch S or switch S is closed, as will appear more fully below.

Z, is inserted to lessen the tuning sensitivity of the circuit and to determine the tuning range thereof. However, this component is optional and may, if desired, be dispensed with. Variable resistors R and R are adjusted, and the other circuit components, connected between points A and B are chosen in accordance with the fundamental frequency which it is desired to generate when either switch S 1 or switch S is closed.

The operation of the circuit of the present invention will now be described. Initially, assume that switches 14 and are in the positions shown in FIG. 2, that is, switch 14 is connected so that differentiator 13 is not in circuit with point X and switch 15 is connected to terminal F of the secondary of transformer T Now, if for example, switch S is depressed in order to select a desired keyboard note, current will flow from B plus source 40 through resistor R the primary of transformer T switch S and diode D to point Z. The current at point Z will be divided into three paths. The first path will include diode D-,, resistor R and diode D This will cause diode D to conduct and present a very low impedance to resistor R The frequency of oscillator 10, will then be determined by the effective resistance between points A and B, which will comprise the series combination of impedance 2,, resistor R and diode D The second current path from terminal Z is through capacitor C, to ground and serves to charge this capacitor to a voltage slightly less than the voltage of B plus source 40. This permits current to continue to flow through diode D after switch S is released and allows the note to remain at its approximate pitch. The third current path from point Z is through diode D to the collector of transistor 0, and to point X, either directly or through differentiator 13, depending upon the position of switch 14. It will be understood, of course, that the foregoing explanation applies equally well to the current paths which exist when switch S is closed with diode D corresponding to diode D diode D corresponding to diode D etc. The only real difference is that the effective resistance between points A and B will be determined by the series combination of impedance 2,, the delta combination of resistor R diode D, and resistor R and diode D When S is first closed, an inrush of current will flow through the primary of transformer T creating a pulse in the secondary of transformer T With switch 15 in the position shown, connected to point F, the current flowing in the secondary of transformer T, will cause transistor Q, to become conductive and the collector emitter impedance thereof will drop to a very low level. This will provide a discharge path through diode D or diode D, for any capacitors which may have remained charged from a previous note. This will include capacitors C C and capacitor C in FIG. 1, whose function was described above. This effect is extremely brief, and has no appreciable effect upon the playing of the new note.

After the note has been played, and S is released, capacitor C which as explained above, has been charged nearly to B plus voltage, begins to discharge slowly through D R and D The discharge rate of capacitor C can be regulated by appropriately choosing a value for resistor R As the voltage on capacitor C decreases, the current fiow through diode D also decreases and the impedance of D rises proportionately. Since D is a series component of the frequency determining resistance between points A and B, the resistance will rise as the impedance of diode D rises and the pitch of the note will consequently fall slightly. Thus, if the person utilizing the keyboard of the present invention, quickly depresses and releases S (or 8,) with switches 14 and 15 in the positions shown, a note characteristic of the string bass will result, characterized by a slightly higher pitch at the beginning of the note than at the end.

It will be realized that the sustain effect of the present invention is accomplished by the charging of capacitor C through the current path including diode D,,, as explained above. After release of switch S (or switch 8,), the amplitude of the note will also decay slowly due to the discharge of capacitor C, through resistor 17. This results in the sustain or legato effect.

In a second mode of operation, when it is desired to create a staccato effect, switch 14 is moved so as to connect differentiator 13 to point X and the base of transistor O is connected to point G in the secondary of transformer T via switch 15. In this mode of operation, the basic current paths are the same as described above. However, with differentiator 13 in the circuit, a gating pulse will be provided only at the inception of the note, since the output of the differentiator will be a steep voltage spike. Therefore, amplitude decay of the note will begin shortly after the key is depressed. When the key is released, the abrupt termination of current in the primary of transformer T, will cause current to flow in the secondary of transformer T, in a direction opposite to that shown by the arrows. This will cause transistor 0, to conduct and apply a very sharp negative voltage spike to capacitor C causing it to discharge. The gate comprising diodes 11 and 12 in FIG. 1 will thus immediately close, preventing the note generated by the oscillator from being fed to the output. Therefore, the note is abruptly terminated when either switch S orswitch S is released, resulting in a staccato effect. The musician, therefore, by utilizing the present invention, will have a wide choice of rhythmic effects, i.e. legato or staccato, depending upon the position of switches 14 and 15.

There has thus been described an improvement in electronic instruments which results in great economy due to the use of a single oscillator to generate a multiplicity of notes, thereby obviating the need for multiple oscillators. In addition, the novel cutoff circuit embodied in transformer T, and transistor Q1, affords an extremely efficient and economical means of cancelling a previously keyed note (pedal-cancel feature) while at the same time the circuit is capable of providing a legato or staccato effect.

While a specific embodiment of the invention has been described, it will be realized by those skilled in the art that various changes may be made therein without departing from the spirit or intent of the inventive concept. Therefore, it is intended that the scope of the present invention be defined only by the claims appended below.

I claim:

1. An electronic musical tone generator comprising:

a. an oscillator having a frequency of oscillation at least in part dependent on the value of a variable resistive component in circuit therewith, said resistive component comprising a plurality of individual elements including at least one diode means;

b. first circuit means including keyboard switch means for interconnecting selected individual elements of said resistinve component including said diode means so as to set said resistive component at a nominal value corresponding to an oscillator frequency related to one of a plurality of musical tones generated by said tone generator; and

c. second circuit means coupled to said first circuit means for automatically varying the value of said resistive component, from said set nominal value, by varying the current flow through said diode means after said keyboard switch is released, so as to audibly diminish said frequency of oscillation as time progresses.

2. The tone generator set forth in claim 1, wherein said means for varying the current flow through said diode means comprises capacitor means.

3. The tone generator set forth in claim 2, further including means for charging said capacitor means when said keyboard switch is closed and means for discharging said capacitor means through said diode means when said keyboard switch is released.

4. The tone generator set forth in claim 3, further including gating means for selectively applying the generated musical tone to an output terminal.

5. The tone generator set forth in claim 4, wherein said gating means comprises a gating capacitor for sustaining the generated tone after said keyboard switch has been released.

6. The tone generator set forth in claim 5, further including means for discharging said capacitor means and said gating capacitor when a keyboard switch is closed.

7. The tone generator set forth in claim 6, wherein said discharging means comprises transformer means and semi-conductor means connected to said transformer means and rendered conductive by current flow through said transformer means.

8. An electronic musical tone generator comprising:

a. an oscillator for generating at least one basic frequency;

b. keyboard switch means for causing said oscillator to generate said basic frequency when said keyboard switch means is closed;

c. an output terminal;

d. means for applying the output of said oscillator to said output terminal; and

e. means coupled to said keyboard switch means for rapidly cutting off said oscillator output at said output terminal in response to the release of said keyboard switch means to create a staccato effect.

9. The musical tone generator set forth in claim 8, wherein said means for applying the output of said oscillator to said output terminal comprises gating means including a gating capacitor, means for charging said gating capacitor and differentiating means selectively connectable to said charging means so that said gating means is actuated only at the inception of a musical tone.

10. The musical tone generator set forth in claim 9, wherein said means for rapid cutoff comprises switching means responsive to the release of said keyboard switch for discharging said gating capacitor.

11. The musical tone generator set forth in claim 10, further including transformer primary means connected to said keyboard switch means and transformer secondary means connected to said switching means.

12. The musical tone generator set forth in claim 11, wherein said switching means comprises a transistor and said transformer secondary means is selectively connectable in opposite senses to the base of said transistor. 

1. An electronic musical tone generator comprising: a. an oscillator having a frequency of oscillation at least in part dependent on the value of a variable resistive component in circuit therewith, said resistive component comprising a plurality of individual elements including at least one diode means; b. first circuit means including keyboard switch means for interconnecting selected individual elements of said resistinve component including said diode means so as to set said resistive component at a nominal value corresponding to an oscillator frequency related to one of a plurality of musical tones generated by said tone generator; and c. second circuit means coupled to said first circuit means for automatically varying the value of said resistive component, from said set nominal value, by varying the current flow through said diode means after said keyboard switch is released, so as to audibly diminish said frequency of oscillation as time progresses.
 2. The tone generator set forth in claim 1, wherein said means for varying the current flow through said diode means comprises capacitor means.
 3. The tone generator set forth in claim 2, further including means for charging said capacitor means when said keyboard switch is closed and means for discharging said capacitor means through said diode means when said keyboard switch is released.
 4. The tone generator set forth in claim 3, further including gating means for selectively applying the generated musical tone to an output terminal.
 5. The tone generator set forth in claim 4, wherein said gating means comprises a gating capacitor for sustaining the generated tone after said keyboard switch has been released.
 6. The tone generator set forth in claim 5, further including means for discharging said capacitor means and said gating capacitor when a keyboard switch is closed.
 7. The tone generator set forth in claim 6, wherein said discharging means comprises transformer means and semi-conductor means connected to said transformer means and rendered conductive by current flow through said transformer means.
 8. An electronic musical tone generator comprising: a. an oscillator for generating at least one basic frequency; b. keyboard switch means for causing said oscillator to generate said basic frequency when said keyboard switch means is closed; c. an output terminal; d. means for applying the output of said oscillator to said output terminal; and e. means coupled to said keyboard switch means for rapidly cutting off said oscillator output at said output terminal in response to the release of said keyboard switch means to create a staccato effect.
 9. The musical tone generator set forth in claim 8, wherein said means for applying the output of said oscillator to said output terminal comprises gating means including a gating capacitor, means for charging said gating capacitor and differentiating means selectively connectable to said charging means so that said gating means is actuated only at the inception of a musical tone.
 10. The musical tone generator set forth in claim 9, wherein said means for rapid cutoff comprises switching means responsive to the release of said keyboard switch for disCharging said gating capacitor.
 11. The musical tone generator set forth in claim 10, further including transformer primary means connected to said keyboard switch means and transformer secondary means connected to said switching means.
 12. The musical tone generator set forth in claim 11, wherein said switching means comprises a transistor and said transformer secondary means is selectively connectable in opposite senses to the base of said transistor. 